Soft neural electrode based on three-dimensional porous graphene foam material and use of three-dimensional porous graphene foam material to prepare bone defect filler

ABSTRACT

The invention provides a neural electrode, including a current generation device, a first and a second electrode. The current generation device is connected to the first and second electrodes through a conductive metal wire respectively. At least one of the first and second electrodes is a graphene electrode. The graphene electrode has soft texture and desirable stability to tolerate the repeated pressing and folding treatment, very high charge injection efficiency, and desirable in vivo stability, and is configured to electrically stimulate tissues and organs such as hearts and nerves to promote electrical stimulation and repair of neurons, to further promote regeneration of neural functions. The invention further provides use of a mineralized three-dimensional porous graphene foam material to prepare a bone defect filler. The bone defect filler has desirable biological compatibility, promotes cell proliferation, and accelerates and induces osteogenic differentiation of bone marrow mesenchymal stem cells.

This application is the National Stage Application of PCT/CN2017/083737,filed on May 10, 2017, which claims priority to Chinese PatentApplication No.: 201610453656.8, filed on Jun. 22, 2016, and ChinesePatent Application No.: 201610598554.5, filed on Jul. 28, 2016, all ofwhich are incorporated by reference for all purposes as if fully setforth herein.

FIELD OF THE INVENTION

The present invention relates to the field of biomedical engineering,and in particular, to a neural electrode based on a three-dimensionalporous graphene foam material and a preparation method of the same anduse of a three-dimensional porous graphene material to prepare a bonedefect filler.

DESCRIPTION OF THE RELATED ART

A basic functional unit of neural activity is a neuron which has thefunctions of receiving a stimulus and conducting an impulse andexcitation. In electrical stimulation therapy, an electrical signalhaving a suitable waveform and frequency is applied to a neuralelectrode to stimulate a neural tissue in direct contact to activateneural activity, to alleviate a dysfunction in a neural system. Apacemaker is an electrotherapeutic instrument implanted in a body. Apulse generator outputs an electrical pulse powered by a battery. A leadelectrode conducts the electrical pulse to stimulate myocardium incontact with the electrode, to excite and contract the heart, to treatsome cardiac dysfunctions caused by irregular heartbeats.

A conventional metal wire electrode such as platinum, gold, and titaniumhas been developing remarkably, but still has the following problems:(1) A rigid electrode material and a soft tissue have very differentmechanical performance, such that it is difficult to match themechanical difference between an electrode material and a soft tissue.(2) The charge injection efficiency is low. (3) The biologicalcompatibility is poor. The development of a novel electrode material issignificant for the clinical use of an implantable neural electrode.

A bone defect means that the structural integrity of a bone iscompromised and is a common clinical disease. The major causes to bonedefects include injuries, infections, tumors, surgical debridement ofosteomyelitis, and various congenital disorders. When a bone defect isexcessively severe or a bone defect occurs on a relatively small bone,such a bone defect heals slowly and poorly, and surgical intervention isrequired. Artificial bone filling is one of the major therapies. Themost basic requirement on artificial bone filling is desirablebiological compatibility, so that immunological rejection responses donot occur.

Graphene is a novel carbon allotropy following the discovery offullerene and carbon nanotubes. Graphene has a unique physical-chemicalstructure and a unique electronic structure. Therefore, graphenemanifests various remarkable performances that conventional materials donot have. For example, graphene has features such as an ultra-largetheoretical specific surface area, desirable electrical and thermalconductivity, and excellent mechanical performance, optical performance,and biological compatibility. Three-dimensional porous graphene inheritsthe excellent properties of two-dimensional graphene and has a largerspecific surface area and provides diverse opportunity for furtherchemical surface modification.

Hydroxyapatite is one of the major inorganic components of bones and iswidely applied to bone tissue engineering. Three-dimensional porousgraphene and hydroxyapatite are combined so that a mineralized materialhas a simulation bone structure, promotes cell proliferation, andaccelerates and induces osteogenic differentiation of bone marrowmesenchymal stem cells.

SUMMARY OF THE INVENTION

To solve the foregoing technical problem, the present invention providesa soft neural electrode based on a three-dimensional porous graphenefoam material and a preparation method of the same. The neural electrodehas high charge injection efficiency and desirable biologicalcompatibility. The present invention further provides use of athree-dimensional porous graphene material to prepare a bone defectfiller and a bone defect filler. The bone defect filler has desirablebiological compatibility, promotes cell proliferation, and acceleratesand induces osteogenic differentiation of bone marrow mesenchymal stemcells.

To achieve the foregoing object, the following technical solutions areused in the present invention.

In an aspect, the present invention provides a soft neural electrodebased on a three-dimensional porous graphene foam material, including acurrent generation device, a first electrode and a second electrode. Thecurrent generation device is connected to the first electrode and thesecond electrode through a conductive metal wire respectively. At leastone of the first electrode and the second electrode is athree-dimensional porous graphene electrode. The graphene electrode isconfigured as a disc or a strip.

Preferably, an insulating protective sleeve is disposed outside theconductive metal wire.

More preferably, the protective sleeve is made of silica gel orpolyurethane, and the thickness of the protective sleeve is between 0.5mm and 3 mm. Preferably, the conductive metal wire is a silver wire or acopper wire, and is more preferably a silver wire.

Preferably, the conductive metal wire is connected to thethree-dimensional porous graphene electrode by a conductive adhesive,and is more preferably a silver adhesive.

Preferably, the three-dimensional porous graphene electrode is providedwith a protective substrate.

Preferably, the protective substrate is formed of a polymer material,and the polymer material is polydimethylsiloxane (PDMS), polyurethane ora polyacrylic acid copolymer, and is more preferably PDMS.

Preferably, the thickness of the protective substrate is 0.1 mm to 2 mm.

Preferably, a thickness ratio of the three-dimensional porous grapheneelectrode to the protective substrate is 1:0.25 to 4. The protectivesubstrate is placed onto one surface of electrode. The other surface ofelectrode is unprotected and the graphene foam material is exposed toavoid the harm of electrical conductivity.

In another aspect, the present invention provides a preparation methodof the foregoing neural electrode based on a three-dimensional porousgraphene foam material, including the steps of:

(1) bonding a three-dimensional porous graphene electrode to aconductive metal wire by a conductive adhesive, and curing theconductive adhesive completely;

(2) immersing a connecting portion of the conductive metal wire and thethree-dimensional porous graphene electrode in a polymer solution, andcuring the polymer to prepare a protective substrate, where a polymermaterial in the polymer solution is selected from polydimethylsiloxane(PDMS), polyurethane or a polyacrylic acid copolymer, and is preferablyPDMS; and

(3) connecting the three-dimensional porous graphene electrode havingthe protective substrate and another electrode to a current generationdevice through a conductive metal wire respectively, to prepare a neuralelectrode.

Graphene is a novel carbon nanomaterial following the discovery offullerene and carbon nanotubes. Graphene has a unique physical-chemicalstructure and a unique electronic structure. Therefore, graphenemanifests various remarkable performances that conventional materials donot have. For example, graphene has features such as an ultra-largetheoretical specific surface area, desirable electrical and thermalconductivity, and excellent mechanical performance, flexibility andelasticity (extensibility of nearly 20%), optical performance, as wellas biological compatibility. Three-dimensional porous graphene inheritsthe excellent inherent properties of two-dimensional graphene and has alarger specific surface area and provides diverse opportunity forfurther chemical surface modification. Therefore, a neural electrodebased on three-dimensional porous graphene foam is constructed to applyelectrical stimulation and treat diseases, to further improve thequality of life of patients, and very high economic value is obtained.

By means of the foregoing technical solution, the present invention atleast has the following advantages:

The present invention provides a flexible and soft neural electrodebased on a three-dimensional porous graphene material and a fabricationmethod of the same. The soft neural electrode includes athree-dimensional porous graphene electrode, so that electricalstimulation can be applied to local regions of tissues and organs. Theneural electrode has a three-dimensional network structure with a highspecific surface area, and has soft texture and desirable stability totolerate the repeated pressing and folding treatment, so that the neuralelectrode can be curled and used. The neural electrode has very highcharge injection efficiency, and is configured to electrically stimulatetissues and organs such as hearts and nerves to promote electricalstimulation and repair of neurons, to further promote restoration ofneural functions. The neural electrode has desirable biologicalcompatibility, and a cell survival rate is high when neurons or neuralstem cells are cultured on the surface. The neural electrode hasdesirable in vivo stability.

In another aspect, the present invention provides use of athree-dimensional porous graphene material to prepare a bone defectfiller, where the three-dimensional porous graphene material is amineralized three-dimensional porous graphene material.

Preferably, a mole ratio of carbon, calcium, and phosphorus in themineralized three-dimensional porous graphene material is 1:0.05:0.03 to1:500:300. The mole ratio is preferably 1:0.5:0.3 to 1:50:30. The moleratio is further preferably 1:1:0.6 to 1:10:6.

Preferably, a hole diameter of the mineralized three-dimensional porousgraphene material is 100 μm to 300 μm, the porosity of the mineralizedthree-dimensional porous graphene material is 99.3±0.5%, and a framewidth forming a three-dimensional void is 100 μm to 200 μm.

Preferably, the coverage of hydroxyapatite in the mineralizedthree-dimensional porous graphene material is 90% to 100%.

Preferably, particle sizes of the hydroxyapatite are between 5 nm and 50μm.

In still another aspect, the present invention also provides apreparation method of the foregoing bone defect filler, including thefollowing steps:

(1) covering a three-dimensional porous graphene support with a filterpaper, and performing mineralization processing, to obtain a mineralizedthree-dimensional porous graphene material;

(2) immersing the mineralized three-dimensional porous graphene materialin a solution to freeze the mineralized three-dimensional porousgraphene material;

(3) cutting the frozen mineralized three-dimensional porous graphenematerial into mineralized three-dimensional porous graphene sheets; and

(4) immersing the mineralized three-dimensional porous graphene sheetsin ethanol, and drying and sterilizing the three-dimensional porousgraphene sheets to obtain the bone defect filler.

Preferably, single mineralized three-dimensional porous graphene sheetis used as the bone defect filler, or a plurality of mineralizedthree-dimensional porous graphene sheets are stacked and used as thebone defect filler.

Preferably, the plurality of mineralized three-dimensional porousgraphene sheets are stacked by bonding using a biomedical adhesive.

Preferably, in the step (2), the solution is selected from water,tert-Butyl alcohol or a combination thereof.

Preferably, in the step (2), the mineralized three-dimensional porousgraphene material is immersed in the solution and frozen at atemperature of −20° C. to −0.1° C.

Preferably, in the step (3), the frozen mineralized three-dimensionalporous graphene material is cut at a temperature of −20° C. to 5° C. toensure an intact form of the three-dimensional porous graphene material.

By means of the foregoing solutions, the present invention at least hasthe following advantages:

The present invention provides use of a mineralized three-dimensionalporous graphene material to prepare a bone defect filler and apreparation method. Hydroxyapatite in a prepared mineralizedthree-dimensional porous graphene material has uniform particles, andthere is no accumulation of excessively large particles. According to afilling requirement, a prepared mineralized three-dimensional porousgraphene sheet is separately used or the prepared mineralizedthree-dimensional porous graphene sheets are stacked and used forfilling various bone defects. The mineralized three-dimensional porousgraphene sheets are soft as filling substances, have high porosity, andthere are inorganic components that are the same as those forming a bonestructure on the surface to simulate a bone structure, and can promotecell proliferation, and accelerate and induce osteogenic differentiationof bone marrow mesenchymal stem cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a neural electrode based on athree-dimensional porous graphene material according to the presentinvention;

FIG. 2 is a schematic view of a three-dimensional porous grapheneelectrode and a protective substrate according to the present invention.

FIG. 3 is a scanning electron microscope image of mineralized grapheneaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be explained in more detail below withreference to the drawings and in connection with embodiments. It shouldbe understood that, the exemplary embodiments and description thereof ofthe invention are used for illustrating the present invention and arenot intended to limit the invention

Referring to FIG. 1 and FIG. 2, a neural electrode in a preferredembodiment of the present invention includes a current generation device1, a first electrode 3 and a second electrode 4. The current generationdevice 1 is connected to the first electrode 3 and the second electrode4 through a conductive metal wire 2 respectively. At least one of thefirst electrode 3 and the second electrode 4 is a graphene electrode.The second electrode 4 is a graphene electrode in this embodiment. Thegraphene electrode has a disc or a strip shape.

To increase a specific surface area and improve a charge injection rateand stability, the graphene electrode 4 is a three-dimensional porousgraphene electrode.

To avoid potential safety hazards, an insulating protective sleeve 5 isdisposed outside the conductive metal wire 2.

Preferably, the protective sleeve 5 is silica gel or polyurethane, andthe thickness of the protective sleeve 5 is between 0.5 mm and 3 mm.

Preferably, the conductive metal wire 2 is a silver wire or a copperwire, and is preferably a silver wire.

Preferably, the conductive metal wire 2 is connected to thethree-dimensional porous graphene electrode by a conductive adhesive,and is preferably a silver adhesive.

To support the three-dimensional porous graphene electrode 4 and protectthe conductive connecting surface of the conductive metal wire 2, thesilver adhesive and the three-dimensional porous graphene electrode 4, aprotective substrate 6 is disposed on one surface of thethree-dimensional porous graphene electrode 4. The other surface ofelectrode is unprotected and the graphene is exposed. The conductiveconnecting surface is connected with and supported by the protectivesubstrate 6.

Preferably, the protective substrate 6 is formed of a polymer material.The polymer material is polydimethylsiloxane (PDMS), polyurethane or apolyacrylic acid copolymer, and is preferably PDMS.

Preferably, the thickness of the protective substrate 6 is 0.1 mm to 2mm.

If the thickness of protective substrate in the three-dimensional porousgraphene electrode 4 is excessively large, the three-dimensional porousgraphene electrode 4 is not soft enough and heavy and thus has poorusability. If the protective substrate 6 is thin, the three-dimensionalporous graphene electrode 4 is not firm and cannot completely preventthe graphene electrode 4 from contacting with a tissue. If theprotective substrate 6 fully covered onto the graphene foam material,making the graphene material insulated with the tissues and organs. Theelectrode 4 cannot work properly. Therefore, a thickness ratio of thethree-dimensional porous graphene electrode 4 to the protectivesubstrate 6 is 1:0.25 to 4.

Embodiment 1

Preparation of a neural electrode based on a three-dimensional porousgraphene material includes the following steps:

(1) A three-dimensional porous graphene electrode 4 was bonded to asilver wire by a silver adhesive, and then was heated to 70° C. suchthat the silver adhesive was completely cured, wherein the thickness ofthe three-dimensional porous graphene electrode 4 is 0.5 mm.

(2) A connecting portion of the silver wire and the three-dimensionalporous graphene electrode 4 was immersed in a PDMS solution, vacuumingwas performed to remove bubbles from the solution, and the temperaturewas kept at 70° C. for 6 h to cure PDMS, then a protective substrate 6with a thickness of 2 mm was prepared. Around 0.2 mm of graphene foammaterial was exposed and 0.3 mm (0.5-0.2=0.3 mm) of graphene foammaterial was protected with PDMS.

(3) The three-dimensional porous graphene electrode 4 with theprotective substrate 6 and a metal titanium electrode were connected toa current generation device 1 through a silver wire respectively, andthen a neural electrode was obtained.

Embodiment 2

Preparation of a neural electrode based on a three-dimensional porousgraphene material includes the following steps:

(1) A three-dimensional porous graphene electrode 4 was bonded to acopper wire by a silver adhesive, and then was heated to 50° C. suchthat the silver adhesive was completely cured, wherein the thickness ofthe three-dimensional porous graphene electrode 4 is 2 mm.

(2) A connecting portion of the copper wire and the three-dimensionalporous graphene electrode 4 was immersed in a PDMS solution, vacuumingwas performed to remove bubbles from the solution, and the temperaturewas kept at 100° C. for 1 h to cure PDMS, then a protective substrate 6with a thickness of 0.5 mm was prepared. 1.5 mm of graphene foam wasexposed. Before PDMS is cured, a heart-shaped mold may be lightlypressed on a graphene surface, to produce a heart-shaped deformation onthe graphene surface. After PDMS is completely cured, a concaveelectrode is obtained to better fit a heart region.

(3) The three-dimensional porous graphene electrode 4 with theprotective substrate 6 and a metal platinum electrode were connected toa current generation device 1 through a copper wire respectively, andthen a neural electrode was obtained.

Embodiment 3

Preparation of a neural electrode based on a three-dimensional porousgraphene material includes the following steps:

(1) A three-dimensional porous graphene electrode was bonded to a silverwire by a silver adhesive, and then was heated to 60° C. such that thesilver adhesive was completely cured, wherein the thickness of thethree-dimensional porous graphene electrode 4 is 1 mm.

(2) A connecting portion of the silver wire and the three-dimensionalporous graphene electrode 4 was immersed in a polyurethane solution,vacuuming was performed to remove bubbles from the solution, thesolution was placed at a room temperature for 24 h to cure polyurethane,wherein a protective substrate with a thickness of about 1 mm wasprepared. And 0.5 mm of graphene foam was exposed.

(3) The three-dimensional porous graphene electrode 4 with theprotective substrate 6 and a metal gold electrode were connected to acurrent generation device 1 through a silver wire respectively, and thena neural electrode was obtained.

Embodiment 4

Preparation of a neural electrode based on a three-dimensional porousgraphene material includes the following steps:

(1) Two three-dimensional porous graphene electrodes were bonded tosilver wires by a silver adhesive respectively, and then were heated to60° C. such that the silver adhesives were completely cured, wherein thethickness of each three-dimensional porous graphene electrode 4 is 1 mm.

(2) A connecting portion between one of the silver wires and thethree-dimensional porous graphene electrode 4 was immersed in apre-polymer solution of polyacrylic acid, vacuuming was performed toremove bubbles from the solution, the solution was irradiated underultraviolet light (10 W) for 6 h to cure polyacrylic acid, where thethickness of an obtained protective substrate 6 is approximately 1 mm.And 0.5 mm of graphene foam was exposed.

(3) The three-dimensional porous graphene electrode 4 with theprotective substrate 6 and the other three-dimensional porous grapheneelectrode were connected to a current generation device 1 through asilver wire respectively, and then a neural electrode was obtained.

The neural electrode of the present invention has the following workingprinciples:

The prepared flexible neural electrode based on three-dimensional porousgraphene is applied to cardiac pacemaker. In the soft and flexibleneural electrode based on three-dimensional porous grapheme, oneelectrode is a three-dimensional porous graphene electrode 4, andanother is a metal titanium electrode. The three-dimensional porousgraphene electrode 4 is implanted in a human's heart for exerting anelectrical pulse to the heart to stimulate the heart to beat. Thesurface of exposed graphene foam is faced to the heart. The metaltitanium in a metal titanium electrode may alternatively be platinum orgold. The metal titanium electrode may also alternatively athree-dimensional porous graphene electrode 4.

The prepared flexible neural electrode based on three-dimensional porousgraphene may further be wound on a nerve for use. A typical use processis as follows: a surgery is performed to expose a nerve, and then athree-dimensional porous graphene electrode 4 in a strip form is lightlywrapped on the nerve. The surface of exposed graphene foam is faced tothe nerve. The surgery should be performed as lightly as possible toavoid fracture of graphene, and then the cut tissue is stitched.

After testing, the flexible neural electrode based on three-dimensionalporous graphene foam has the following effects: a charge injectionamount in a unit area is 3 to 100 times that of a conventionalelectrode. When nerve cells are cultured on the surface, a cell survivalrate is higher than 90%. An end surface of graphene may be curled foruse. After graphene is curled by 100 times, a resistance change is lessthan 50%. After graphene is implanted in a body, a resistance change isless than 200% in three months.

Embodiment 5

The preparation of a mineralized three-dimensional porous graphene foammaterial includes the following steps:

(1) Three-dimensional porous graphene foam material was fabricated bychemical vapor deposition (CVD) with three-dimensional porous nickel ascatalyst. After removing the nickel catalyst, and a three-dimensionalporous graphene foam scaffold was obtained.

(2) O₂ plasma treatment was performed on the three-dimensional porousgraphene scaffold for 3 min to 5 min, and then the three-dimensionalporous graphene scaffold was covered with a filter paper.

(3) 2 mmol to 100 mmol bicarbonate ions were added to a simulated bodyfluid with a tenfold concentration (the simulated body fluid with atenfold concentration is formed of compounds such as NaCl, CaCl₂, MgCl₂,NaHCO₃ and Na₂HPO₄), filtering was performed by using a filtering systemwith a 0.22 μm hole diameter, then the three-dimensional porous graphenesupport was placed on a decoloring shaker for 1 h to 12 h at a roomtemperature, and a mineralized three-dimensional porous graphenematerial was obtained, and finally the mineralized three-dimensionalporous graphene material was washed with water and ethanol.

A mole ratio of carbon, calcium and phosphorus in the mineralizedthree-dimensional porous graphene material is 1:0.05:0.03 to 1:500:300.The mole ratio is preferably 1:0.5:0.3 to 1:50:30. The mole ratio isfurther preferably 1:1:0.6 to 1:10:6. A hole diameter of the mineralizedthree-dimensional porous graphene material is 100 μm to 300 μm. Theporosity of the mineralized three-dimensional porous graphene materialis 99.3±0.5%. A frame width forming a three-dimensional void is 100 μmto 200 μm. The coverage of hydroxyapatite in the mineralizedthree-dimensional porous graphene material is 90% to 100%. Particlesizes of the hydroxyapatite are between 5 nm and 50 μm. The mineralizedthree-dimensional porous graphene material was characterized by scanningelectron microscope.

Specifically, 10 mmol bicarbonate ions were added to a simulated bodyfluid with a tenfold concentration, and the simulated body fluid is thenplaced for 4 h, and a mole ratio of carbon, calcium and phosphorus inthe obtained mineralized three-dimensional porous graphene material is1:0.5:0.3 to 1:2:1.2. The coverage of hydroxyapatite in the mineralizedthree-dimensional porous graphene material is 90% to 95%. Particle sizesof the hydroxyapatite are between 5 nm and 1 μm, and the porosity of thehydroxyapatite is 99.3±0.5%. The obtained material is shown in FIG. 3.The crystal in FIG. 3 shows that the three-dimensional porous graphenesupport is successfully mineralized.

100 mmol bicarbonate ions were added to the simulated body fluid with atenfold concentration, and the simulated body fluid is then placed for0.5 h, and a mole ratio of carbon, calcium and phosphorus in theobtained mineralized three-dimensional porous graphene material is 1:5:3to 1:20:12. The coverage of hydroxyapatite in the mineralizedthree-dimensional porous graphene material is 95% to 100%. Particlesizes of the hydroxyapatite are mostly between 50 nm and 20 μm. Someparticles of the hydroxyapatite agglomerate, particle sizes ofagglomerated particles are about 50 μm, and the porosity of thehydroxyapatite is 98±1%.

Embodiment 6

Preparation of a bone defect filler using a mineralizedthree-dimensional porous graphene material.

The mineralized three-dimensional porous graphene material of theembodiment 5 was immersed in water, after freezing at −20° C., themineralized three-dimensional porous graphene material was cut intosheets at −10° C., then the mineralized three-dimensional porousgraphene sheets were immersed in 75% ethanol, dried, and radiated forsterilization to obtain the bone defect filler.

Embodiment 7

Preparation of a bone defect filler using a mineralizedthree-dimensional porous graphene material.

The mineralized three-dimensional porous graphene material of theembodiment 5 was immersed in tert-Butyl alcohol, after freezing at −0.1°C., the mineralized three-dimensional porous graphene material was cutinto sheets at 5° C., then the mineralized three-dimensional porousgraphene sheets were immersed in 75% ethanol, washed with pure ethanol,dried, and radiated for sterilization to obtain the bone defect filler.

Embodiment 8

Preparation of a bone defect filler using a mineralizedthree-dimensional porous graphene material.

The mineralized three-dimensional porous graphene material of theembodiment 5 was immersed in a 50% aqueous solution of tert-Butylalcohol, after freezing at −5° C., the mineralized three-dimensionalporous graphene material was cut into sheets at 0° C., then themineralized three-dimensional porous graphene sheets were immersed in75% ethanol, washed with water, washed with pure ethanol, freeze-driedat low temperature, and radiated for sterilization to obtain the bonedefect filler.

According to the clinical requirements, a single sheet is used, or aplurality of sheets are stacked or bonded by a biomedical liquid, forfilling bone defects having various shapes.

As compared with a hydroxyapatite biological ceramic that is used as aconventional synthetic bone replacement, when the mineralizedthree-dimensional graphene sheet is used as a bone defect filler, thebiological compatibility, bone conductivity, and osteogenic inductionability are more desirable, and during the culture of mesenchymal stemcells on surface, the proportion of mesenchymal stem cells thatdifferentiate into osteogenic cells is 2 times to 20 times larger, andthe differentiation time is earlier by 1.1 times to 5 times.

Compared with a hydroxyapatite biological ceramic (a control group) thatis used as a bone defect filling material, when the mineralizedthree-dimensional porous graphene sheets (an experimental group) areused as bone defect filling materials, in one month to three monthsafter filling in bone defect regions, the bone density changes fasterthan that in the control group. After three to six months, the bonedensity in the experimental group can reach 60% to 90% of the originalbone density, and the bone density in the control group is only 30% to60%. The bone density in the experimental group is 1.1 times to 5 timesof the bone density in the control group. As observed in a CT image,there is no clear interface in the experimental group, but there is adistinct bone-material interface in the control group.

The above preferred embodiments are described for illustration only, andare not intended to limit the scope of the invention. It should beunderstood, for a person skilled in the art, that various improvementsor variations can be made therein without departing from the spirit andscope of the invention, and these improvements or variations should becovered within the protecting scope of the invention.

What is claimed is:
 1. A neural electrode based on a three-dimensionalporous graphene foam material, consisting of a current generationdevice, a first electrode, a second electrode, conductive adhesive,conductive metal wire, a protective substrate, and an insulatingprotective sleeve; the current generation device being connected to thefirst electrode and the second electrode through a conductive metal wirerespectively, wherein at least one of the first electrode and the secondelectrode is a three-dimensional porous graphene electrode, wherein theinsulating protective sleeve is disposed directly outside the conductivemetal wire, and wherein the protective substrate is disposed on onesurface of the three-dimensional porous graphene electrode and formed ofa polymer material.
 2. The neural electrode based on a three-dimensionalporous graphene foam material as claimed in claim 1, wherein theprotective sleeve is made of silica gel or polyurethane.
 3. The neuralelectrode based on a three-dimensional porous graphene foam material asclaimed in claim 1, wherein the conductive metal wire is a silver wireor a copper wire.
 4. The neural electrode based on a three-dimensionalporous graphene foam material as claimed in claim 1, wherein theconductive metal wire is connected to the three-dimensional porousgraphene electrode by a conductive adhesive.
 5. The neural electrodebased on a three-dimensional porous graphene foam material as claimed inclaim 1, wherein the thickness of the protective substrate is 0.1 mm to2 mm.
 6. The neural electrode based on a three-dimensional porousgraphene foam material as claimed in claim 1, wherein a thickness ratioof the three-dimensional porous graphene electrode to the protectivesubstrate is 1:0.25 to 1:4.
 7. A preparation method of the neuralelectrode based on a three-dimensional porous graphene foam material asclaimed in claim 1, comprising steps of: (1) bonding a three-dimensionalporous graphene electrode to a conductive metal wire by a conductiveadhesive; (2) immersing a connecting portion of the conductive metalwire and the three-dimensional porous graphene electrode in a polymersolution, and curing the polymer to form a protective substrate; (3)connecting the three-dimensional porous graphene electrode having theprotective substrate to another electrode and a current generationdevice through conductive metal wire to fabricate the neural electrode;wherein an insulating protective sleeve is disposed directly outside allconductive metal wire.